1. Field of the Invention
This disclosure relates to an image forming apparatus configured to form an image on a sheet.
2. Description of the Related Art
In the related art, an image forming apparatus including a sensor provided at a position downstream of a fixing unit in a direction of sheet conveyance and configured to detect a paper jam in the fixing unit or a delay of a sheet conveyed to the fixing unit is known. The fixing unit is configured to heat and fix toner images to sheets. For example, JP-A-11-125983 discloses an image forming apparatus including an optical sensor as the sensor described above, and a detection lever having a sheet detecting portion mounted on a pivotal shaft of the detection lever and a sensor activating portion mounted on the pivotal shaft of the detection lever. The detection lever is configured to be rotated (pivoted) about the pivotal shaft by a contact of the sheet detecting portion with a sheet and block and allow entry of light to a light-receiving portion of the optical sensor by the sensor activating portion in accordance with a rotating action of the detection lever.
However, the optical sensor may cause an erroneous operation due to moisture vapor generated from a sheet at the time of heat fixation, a failure due to radiant heat generated at the time of heat fixation, or the like. In recent years, the amount of moisture vapor generated from the sheet at the time of heat fixation per unit time is now increasing in association with an increase in printing speed. Therefore, there is a demand for an arrangement of the optical sensor at a position less susceptible to the moisture vapor generated from the sheet at the time of heat fixation and to the radiation heat at the time of heat fixation.
Here, in an apparatus having an openable-and-closable door arranged in the vicinity of a fixing unit, a configuration in which an optical sensor is arranged in a door (see JP-A-61-193159) to prevent an increase in size of an entire image forming apparatus while arranging the optical sensor at a position far from the fixing unit is conceivable. In order to arrange the optical sensor at a position far from a heat source of the fixing unit, the length of an arm of the sheet detecting portion and the length of an arm of the activating portion need to be long. However, if the arm of the detection lever is long in a case where the optical sensor is arranged in the door, a large amount of the arm sticks out when the door is opened. If a large amount of the arm of the detection lever sticks out when the door is opened, the user may touch the arm with no discretion. Therefore, the likelihood of breaking the detection lever is increased.